1. Field of the Invention
The present invention relates to a dispersant having a multifunctional head and a phosphor paste composition comprising the dispersant. More specifically, the present invention relates to a dispersant having a multifunctional head that comprises an acidic group, a basic group and an aromatic group, thereby enhancing an affinity for the surfaces of a variety of phosphor particles and thus improving dispersibility.
2. Description of the Related Art
In recent years, a variety of display devices have been developed and widely used as substitutes for cathode ray tubes (CRTs). Such display devices include flat panel displays (FPDs), such as, for example, liquid crystal displays (LCDs), plasma display panels (PDPs), electro-luminescent displays (ELDs), field emission displays (FEDs), and vacuum fluorescent displays (VFDs). Such display devices can be used for exterior decorations or display parts of electronic appliances, e.g., exterior decorations or keypads of cellular phones.
It is desirable for such display devices to include a fluorescent screen. The luminescent properties of the display devices can be varied depending upon the physical properties. In other words, although a phosphor inherently has a high luminance, unless a fluorescent film made of the phosphor is suitably formed, the display device including the fluorescent film cannot exhibit high luminance.
A fluorescent film is generally produced by homogeneously applying a phosphor paste composition to a supporting substrate, followed by drying the phosphor paste composition. In general, phosphor paste compositions comprise a solvent, a binder and a phosphor and selectively comprise a dispersant for improving dispersibility of the phosphor.
The dispersant improves dispersibility of the phosphor, which leads to a lower viscosity. Thus by improving dispersibility, it is possible to increase the amount of the phosphor present in a given fluorescent film and to thereby increase the packing density of the phosphor in a fluorescent film. Thus the efficiency of fluorescence can be increased over a comparative film having an equivalent thickness, but having a lower packing density. Using a dispersant also permits an increase in the stability of a paste that can be used in a printing process.
Dispersants that are surfactants include a head and a tail. The head must have an affinity for a dispersoid to be dispersed in the dispersion media. The tail must have an affinity for a dispersion media capable of dispersing the dispersoid. In addition, it is desirable to use a dispersant capable of keeping adjacent phosphor particles apart from each other. In other words, it is desirable for the dispersant to prevent the phosphor particles from agglomerating with one another.
Commercially available dispersants for a phosphor have a monofunctional head generally comprise either an acidic group, or a basic or aromatic groups, and thus can disperse only specific phosphors having an affinity for selected functional group that are attracted to either the acidic group or the basic or the aromatic groups.
Accordingly, to improve the luminescent properties of display devices, there is an increasing demand to develop a novel dispersant for a phosphor that is capable of being applied to a variety of phosphors, e.g., organic phosphors, and exhibits superior dispersibility.